1. Field of the Invention
This invention relates to a camera module, and more specifically to a camera module that can be used in small-sized electronic apparatuses such as digital cameras, camera-equipped cellular phones and the like.
2. Description of the Related Art
A camera module having a function of displacing a lens unit in a direction of an optical axis of the lens unit is used in relatively small-sized digital cameras, camera-equipped cellular phones and the like. This function is used for providing an autofocus function and/or zoom function and the like, and is achieved by an interaction between a magnetic field generated by an electrical current flowing in a coil and a magnetic field generated by a yoke and magnets provided on the yoke.
Such a camera module generally includes a barrel which holds the lens unit, a holder which houses the barrel therein, and a pair of leaf springs for supporting the holder so that the holder is displaceable in a direction of an optical axis of the lens unit.
FIG. 3 is an exploded perspective view of an autofocus actuator assembly 100 used in a conventional camera module for displacing a lens unit (not shown) in a direction of an optical axis thereof. It is to be noted that an imaging element (not shown) is provided below a base 111 of the actuator assembly 100.
A holder 108 that houses a barrel (not shown) holding the lens unit is provided in a space between a cover 101 and the base 111 so that the holder 108 is displaceable in a direction of an optical axis of the lens unit together with the lens unit.
An inner annular portion 104b of an upper leaf spring 104 and an inner annular portion 110b of a lower leaf spring 110 are attached to upper and lower cylindrical end portions of the holder 108, respectively, using an adhesive. Further, an outer annular portion 104a of the upper leaf spring 104 is attached to a top surface of a yoke 105 and an outer annular portion 110a of the lower leaf spring 110 is provided on a lower end of the yoke 105, respectively. Furthermore, on the upper surface of the inner annular portion 104b of the upper spring 104 which is attached to the upper cylindrical end portion of the holder 108, a stopper denoted by the reference numeral 102 is attached using an adhesive.
Three bridge portions 104c are coupled between the outer annular portion 104a and the inner annular portion 104b of the upper leaf spring 104. As is the same with the upper leaf spring 104, three bridge portions 110c are coupled between the outer annular portion 110a and the inner annular portion 110b of the upper leaf spring 110. By resilient deformation of the respective three bridge portions 104c and 110c, the holder 108 can be displaced in a direction of an optical axis of the lens unit.
A plurality of magnets 106 are provided on the yoke 105 so as to produce a magnetic field. The yoke 105 has an axial bore 105a for receiving the holder 108. Further, a coil 107 is provided around an outer periphery of a cylindrical portion of the holder 108 so that the coil 7 is disposed in the magnetic field produced by the magnets 106 and the yoke 105 in a state that the holder 108 is received in the axial bore 105a. By supplying a current to the coil 107 to generate a magnetic field, the holder 108 can be displaced in a direction of an optical axis of the lens unit by a driving force generated by the interaction of the magnetic fields. In this regard, it is to be noted that a component donated by the reference numeral 109 in FIG. 3 is a ring-shaped plate provided between the lower leaf spring 110 and the lower end of the yoke 105. Further, a flexible printed circuit board 103 for supplying an electrical current to the coil 107 is provided below the outer annular portion 110a of the lower leaf spring 110.
As shown in FIG. 4, the base 111 has a base upper surface 111c having an opening 111a at a center thereof defined by an edge 111b, and the base upper surface 111c is formed into a flat surface continued to the edge 111b. 
In the actuator assembly 100 described above, the components such as the cover 101, the stopper 102, the holder 108 and the base 111 are molded parts made of synthetic resins containing glass filler as aggregate.
It is to be noted that an actuator assembly similar to the actuator assembly 100 described above is disclosed in JP-A-No. 2004-280031.
As described above, the actuator assembly 100 includes the components such as the cover 101, the stopper 102, the holder 108 and the base 111 which are made of synthetic resins containing glass filler as aggregate. Therefore, when the small-sized electronic apparatuses equipped with the camera module is dropped by an accident, there is a case that dust which is formed from glass filler or synthetic resins chipped from the molded parts is generated. If such dust is generated, there is a case that such dust is fallen onto the base upper surface 111c of the base 111, then fallen into the opening 111a over the edge 111b, and finally fallen onto a surface of an upper lid glass (not shown) disposed in an imaging area including the imaging element. If such dust is fallen onto the surface of the lid glass and adheres thereto, there arises a problem in that burred dots appear on an image obtained by the camera module.